Three light switch riddle, help.

I may be missing something, but what I heard was you have a house that you may own for free if you can figure out the light switches. There are three switches downstairs, and one lights the lamp in the attic. With only one trip upstairs, how do you figure out what one turns on the lamp?


SSG Schwartz

Assuming the light upstairs starts in the off position: Flip switch A on, leave it on for a short while, then flip it off and flip switch B on. Go upstairs: if the light is on, switch B controls it. If it’s off, bring your hand to feel it: if it’s warm, switch A controls it; otherwise, C.

Turn one on for 5 or 10 minutes, then turn it off and turn another one on. Then go up to the attic - if the light’s on, the switch that’s on controls it. If it’s off, see if the bulb is warm. If so, the one you switched on and off controls it. Otherwise, it’s the final one.

Alternate solution for smartasses like me: Use your one trip upstairs to replace the bulb with a buzzer. Then, when you go back downstairs, flip the switches one by one until you hear your buzzer go off. This has the added benefit of working for any number of switches and is independent of the initial state of the bulb.

Given that the whole thing basically hinges on some mild smartassery anyway, I don’t think anyone can really impugn Q.E.D.'s solution. :slight_smile:

Send someone upstairs. Flip switches until you hear; “it’s on!”

Staying downstairs, first turn each of the switches on and off to eliminate the one that lights the downstairs light.

Then switch on one of the other two. Go to the attic. If the light’s on you’ve got it. If the light’s off it’s the off switch that doesn’t light the first floor light.

I wonder what the third switch does…

Actually, since I’ve always lived in multi-story homes, I assumed you have First Floor Light, Second Floor Light and Attic Light.

Or maybe Cellar Light, First Floor Light, Attic Light.

In any case once you eliminate the first floor one, a trip upstairs can tell you which of the other two lights what.

See, but this is a riddle, not a description of an actual house lighting setup. Typically, depending upon which version of the riddle you’re reading, only one of the switches does anything at all, which is to turn on the upstairs light. The other two are (or are taken to be) dummies, not doing anything observable.

Well, based on the “riddle” as explained in the OP there nothing saying that only one of the switches actually works.

I was assuming the riddle’s “trap” was that folks assumed that they could only set the light switches once or they forgot that one of the switches must light the downstairs where they are at the start.

The riddle with only one working switch is more of a “what do I have in my pocket?” riddle.

Not at all; it has a definite practical solution, as outlined in posts #2 and #3. This is one of the typical wordings for this riddle.

Yes, answers two and three are both ways to answer the riddle that you just linked to.

But that riddle gives more limiting conditions, which the OP’s telling of the riddle did not have.

In the OP’s riddle, you may win “the house” if you figure out the switches, which are obviously downstairs. One of the lights the attic. Those are the only conditions. I don’t think in that case I was wrong to assume one of the switches lights the downstairs of “the house.”

Again, I would not want to impugn VernWinterbottom’s solution. It’s only “fault” is that it’s not the particular cheap trick the questioner is expecting; but that’s really no fault at all.

Again with the OP’s scenario of switches downstairs and the light in the attic, you could do it with no trips upstairs by waiting until dark and looking at the attic window when you flip the switches.

I have owned a couple of old houses with “mystery” switches. They serve no purpose and/or their purpose is lost to time and known only to God. They control nothing and do nothing.

It reminds me of the commercial where the guy is flipping a switch and asking his none too interested wife if lights are going on/off. Then we pan out to see the neighbor’s garage door going up and down on her car. That is what my switches were like…

That commercial always reminded me of the Steven Wright joke which preceded it.

They probably control a random outlet (possibly an outlet on the outside of the house) that has nothing hooked up to it, and so appears to do nothing.

I had one of those. It’s in the upper part of a closet. It’s one of those old switches that lights up when it’s off, and the little bulb in the switch only works intermittently - just often enough to remind me that the switch still has power to it. Eventually, I figured out that it went to a tiny little attic fan that couldn’t possibly accomplish anything, and had a thermostat on it. Either the thermostat or fan is defunct, I never left the switch on long enough for the attic fan to come on, or I didn’t notice it running.

This riddle inherently requires an outside-the-box solution, which always makes it amusing when someone claims “No, that’s not the correct outside-the-box solution; this one is”. They’re not thinking outside the proverbial box; they’re just thinking inside a different box.

Of course, even the simplest inside-the-box solution as the OP has phrased it still gives you a 2 in 3 chance of guessing right, which is pretty good odds for winning a free house.
For ages, my mom’s house had a dummy switch in the living room (in the middle of a three-switch panel, between two functional switches), and also had a lighting fixture in the living room ceiling that had no means of turning on. A couple of years ago, she finally found a way to connect them to each other without ripping out the entire ceiling.